In general, a large-sized transporter vehicle called a dump truck has a liftable vessel (loading platform) on a frame of a vehicle body, and transports crushed stones or the like in a state of a heavy baggage being loaded in a large quantity on the vessel.
Therefore, each travel drive device for driving drive wheels of the dump truck for traveling is provided with a cylindrical axle housing mounted in a non-rotating state on a vehicle body, a rotational shaft provided to axially extend in the axle housing and driven by a drive source such as an electric motor for rotation, a wheel mounting cylinder which is rotatably mounted on an end-side periphery of the axle housing through bearings and to which vehicle wheels are mounted, and a reduction gear mechanism provided between the wheel mounting cylinder and the axle housing to decelerate rotation of the rotational shaft, which is transmitted to the wheel mounting cylinder (Patent Documents 1 and 2).
A wet brake formed of a wet multi-plate type of hydraulic brake for applying a braking force to the rotation of the wheel mounting cylinder and a floating seal arranged between the wet brake and the bearings for retaining a cooling liquid of the wet brake in a sealed state to the wheel mounting cylinder are provided between the axle housing and the wheel mounting cylinder.